Aeration of the water in ponds, lakes, and other bodies water is essential for providing an environment which will support aquatic creatures and plants. The dissolved oxygen supply in such bodies of water is continuously being used by fish, plants, etc. to not only sustain life but to remove waste products formed by decaying organic material and waste products from live organisms.
Dissolved oxygen is removed from the water by these living organisms and replenished by aquatic plants undergoing photosynthesis. As photosynthesis occurs, the plants give off oxygen and use carbon dioxide. As the plants or other aquatic life thrive, more waste products are produced which in turn, raises the biological and chemical oxygen demand. Where the growth rate is rapid, and sunlight cannot reach the organisms, no photosynthesis occurs and less oxygen is produced to help the indigenous flora degrade harmful by-products such as ammonia, methane, etc.
This is especially important in establishments such as fish hatcheries, where oxygen stress makes the fish more susceptible to disease and parasites. Fish may also be killed due to the low oxygen/high ammonia concentration, where the oxygen concentration drops below three or four parts per million. Proper oxygenation also reduces over concentration of algae and decaying matter which can cause musky smells surrounding ponds and an off-flavor in fish.